Theoretical optimization of solar electricity using a DC-microgrid

This master thesis contributed to a project financed by the Swedish Energy Agency and managed by the housing company Eksta AB in collaboration with the consulting Company WSP. The main aim of this master thesis was to perform a theoretical optimization on the usage of own used solar electricity by transferring the surplus PV between buildings in a demonstration area in a DC-microgrid. To achieve this objective, the Swedish regulatory framework for concession was analyzed in order to find exceptions that allow the transfer of solar electricity surplus between buildings in the same real state. A demonstration area belonging to Eksta and located in Fj¨ar˚as, Kungsbacka, was used in order to simulate the transfer of solar electricity surplus. The area consisted of four new residential buildings, one substation, a preschool, a community living, a retirement home and Eksta’s expedi- tion building. The regulation 2007:215 presents the exceptions for the Swedish electricity law (1997:857). The exceptions 22A and 30 from the regulatory framework for concession stated that an internal power line, allowing the transmission of electricity between facilities, could be built when connecting to electrical production facilities. These exceptions were inter- preted as valid for the demonstration area although not all buildings generated solar electricity. The electricity usage and solar electricity generation for each building varied dependent on the building’s purpose and PV system design. When combining all Buildings in a DC-microgrid the electricity usage and PV generation were summarized leading to a more homogeneously distributed consumption and higher solar electricity generation. As a consequence, the own usage rate and self-sufficiency rate were increased by 32 and 6 percentage points compared to the current individual system. In a DC-microgrid the solar electricity surplus accounted for 9% of the total PV generation compared to 41% if not interconnected. The difference was calculated to an optimization of 27 000 kWh/year which represented the demonstration area’s total electricity usage that could come from solar electricity instead of delivered from the grid. Further optimization of the own-used solar electricity could be achieved by maximizing profitable PV roof areas, increasing the electricity efficiency and connecting the solar electricity surplus to a common energy storage system.The energy transition is accelerating in Sweden and in several other countries in the world. As stated in the context of the German “Energiwende”:” There are reasons to switch to renewable energy and to increase energy conservation, and there are reasons to do so now”. 1 Solar energy plays and important role to successfully achieve this transition, but to increase its usage, technology innovation must be supported by regulatory frameworks and economic incentives. The current Swedish electricity law prohibits the transmission of solar electricity between buildings in the same real state. As a consequence, the surplus photovoltaic (PV) is delivered into the grid, which reduces the electrical and economic efficiency of the solar electricity by having to pay variable costs such as energy tax, network charge or VAT. This regulatory framework hampers the full deployment of new innovative microgrid solutions, which have the potential to optimize the self-usage of solar electricity. This master thesis aimed to perform a theoretical optimization of solar electricity by using a direct current (DC) microgrid. Surplus PV was transferred between buildings in a demonstration area, instead of delivered into the grid, in order to analyze the change in own-used solar electricity. The demonstration area was located in Fjärås, Kungsbacka, comprised of a preschool, a community living, a retirement home, Eksta’s AB expedition building and four new residential buildings. The project was performed in collaboration with the housing company Eksta AB and the consulting company WSP. The analysis concluded that when combining the electricity usage and solar electricity generation of all buildings, the electricity use was substantially optimized. The surplus PV accounted for 9% of the total PV generation compared to 41% if not interconnected. This means that by using a DC-microgrid, 27 000 kWh/year solar electricity was directly used by the buildings in the demonstration area instead of delivered into the grid. These technical findings were complemented by a legal case study, indicating that two exceptions from the Swedish regulatory framework for concession would be valid in order to transfer surplus PV between buildings in a demonstration area using a DC- microgrid. In conclusion, the electrical, economic and environmental efficiency of the PV system increased when the solar electricity surplus was transferred between the buildings in a DC- microgrid. In other words, microgrid solutions are important tools to optimize and increase the solar electricity usage, thereby contributing to the energy transition. To fully exploit this systemic microgrid approach, Sweden could further strengthen the regulatory and economic incentives